* Astronomy

Blobrana · L

RE: Leo P

Blobrana · L

Title: ALFALFA Discovery of the Nearby Gas-rich Dwarf Galaxy Leo P. V. Neutral Gas Dynamics and Kinematics
Author: Elijah Z. Bernstein-Cooper, John M. Cannon, Edward C. Elson, Steven R. Warren, Jayaram Chengalur, Evan D. Skillman, Elizabeth A. K. Adams, Alberto D. Bolatto, Riccardo Giovanelli, Martha P. Haynes, Kristen B. W. McQuinn, Stephen A. Pardy, Katherine L. Rhode, John J. Salzer

We present new HI spectral line imaging of the extremely metal-poor, star-forming dwarf irregular galaxy Leo P. Our HI images probe the global neutral gas properties and the local conditions of the interstellar medium (ISM). The HI morphology is slightly elongated along the optical major-axis. We do not find obvious signatures of interaction or infalling gas at large spatial scales. The neutral gas disk shows obvious rotation, although the velocity dispersion is comparable to the rotation velocity. The rotation amplitude is estimated to be V_c = 15 +/- 5 km/s. Within the HI radius probed by these observations, the mass ratio of gas to stars is roughly 2:1, while the ratio of the total mass to the baryonic mass is ~15:1. We use this information to place Leo P on the baryonic Tully-Fisher relation, testing the baryonic content of cosmic structures in a sparsely populated portion of parameter space that has hitherto been occupied primarily by dwarf spheroidal galaxies. We detect the signature of two temperature components in the neutral ISM of Leo P; the cold and warm components have characteristic velocity widths of 4.2 +/- 0.9 km/s and 10.1 +/- 1.2 km/s, corresponding to kinetic temperatures of ~1100 K and ~6200 K, respectively. The cold HI component is unresolved at a physical resolution of 200 pc. The highest HI surface densities are observed in close physical proximity to the single HII region. A comparison of the neutral gas properties of Leo P with other extremely metal-deficient (XMD) galaxies reveals that Leo P has the lowest neutral gas mass of any known XMD, and that the dynamical mass of Leo P is more than two orders of magnitude smaller than any known XMD with comparable metallicity.

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Title: ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo~P. II. Optical Imaging Observations
Authors: Katherine L. Rhode, John J. Salzer, Nathalie C. Haurberg, Angela Van Sistine, Michael D. Young, Martha P. Haynes, Riccardo Giovanelli, John M. Cannon, Evan D. Skillman, Kristen B. W. McQuinn, Elizabeth A. K. Adams

We present results from ground-based optical imaging of a low-mass dwarf galaxy discovered by the ALFALFA 21-cm HI survey. Broadband (BVR) data obtained with the WIYN 3.5-m telescope at Kitt Peak National Observatory (KPNO) are used to construct colour-magnitude diagrams of the galaxy's stellar population down to V_0 ~ 25. We also use narrowband H-alpha imaging from the KPNO 2.1-m telescope to identify an HII region in the galaxy. We use these data to constrain the distance to the galaxy to be between 1.5 and 2.0 Mpc. This places Leo P within the Local Volume but beyond the Local Group. Its properties are extreme: it is the lowest-mass system known that contains significant amounts of gas and is currently forming stars.

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Blobrana · L

Title: ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo P. I. HI Observations
Authors: Riccardo Giovanelli, Martha P. Haynes, Elizabeth A. K. Adams, John M. Cannon, Katherine L. Rhode, John J. Salzer, Evan D. Skillman, Elijah Z. Bernstein-Cooper, Kristen B. W. McQuinn

The discovery of a previously unknown 21cm HI line source identified as an ultra-compact high velocity cloud in the ALFALFA survey is reported. The HI detection is barely resolved by the Arecibo 305m telescope ~4' beam and has a narrow HI linewidth (HPFW of 24 km/s). Further HI observations at Arecibo and with the VLA corroborate the ALFALFA HI detection, provide an estimate of the HI radius, ~1' at the 5 x 10^19 cm^-2 isophote, and show the cloud to exhibit rotation with an amplitude of ~9.0 ± 1.5 km/s. In other papers, Rhode et al. (2013) show the HI source to have a resolved stellar counterpart and ongoing star forming activity, while Skillman et al. (2013) reveal it as having extremely low metallicity: 12 + log(O/H) = 7.16 ± 0.04. The HI mass to stellar mass ratio of the object is found to be 2.6. We use the Tully-Fisher template relation in its baryonic form (McGaugh 2012) to obtain a distance estimate D = 1.3 (+0.9,-0.5) Mpc. Additional constraints on the distance are also provided by the optical data of Rhode et al. (2013) and McQuinn et al. (private communication), both indicating a distance in the range of 1.5 to 2.0 Mpc. The three estimates are compatible within their errors. The object appears to be located beyond the dynamical boundaries of, but still in close proximity to the Local Group. Its pristine properties are consistent with the sedate environment of its location. At a nominal distance of 1.75 Mpc, it would have an HI mass of ~1.0 x 10^6 solar masses, a stellar mass of ~3.6 x 10^5 solar masses, and a dynamical mass within the HI radius of ~1.5 x 10^7 solar masses. This discovery supports the idea that optically faint - or altogether dark - low mass halos may be detectable through their non-stellar baryons.

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Blobrana · L

Astronomers Discover New Neighbour Galaxy to the Milky Way

Leo P is a dwarf galaxy that astronomers have just discovered in the Milky Way's vicinity. At a distance of some five million or six million light-years from the Milky Way, Leo P is not quite a next-door neighbour, but on the vast scales of the universe it counts as a neighbour nonetheless.
Intriguingly, Leo P seems to have kept to itself, rarely if ever interacting with other galaxies. So the discovery, detailed in a series of studies in The Astronomical Journal, offers astronomers a rare glimpse at a cosmic object unsullied by disruptive galactic encounters. It also suggests the presence of other small galaxies that await discovery in our corner of the cosmos.
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